The present invention relates to testing of storage batteries. More specifically, the invention relates to measuring temperature of an electrochemical cell or battery.
When testing or evaluating the performance of cells and batteries, it is desirable to accurately know battery temperature in order to apply appropriate temperature corrections to the measured results. For example Champlin, in U.S. Pat. No. 3,909,708, describes setting a dial on the tester to the battery's temperature in order to cause the measured dynamic conductance to comport with that of a battery at room temperature. However, exactly how this battery temperature information is to be obtained is not discussed. Others employ a very rough correction by instructing the user to push a button when the ambient temperature is, e.g., "below 0.degree. C.". Marino et al., in U.S. Pat. No. 4,423,378 refer to a battery temperature "probe" whose output is inputted to a microprocessor for the purpose of correcting load-test results. Similar temperature probes are described by Alber et al. in U.S. Pat. No. 4,707,795. Other workers have attached thermistors to test clips so that they would be in thermal contact with a battery terminal, or have placed them in thermal contact with the battery's case. Even infrared techniques have been used to determine battery case temperature.
All of these prior art techniques have measured either the battery's ambient temperature or its external case temperature. Unfortunately however, these quantities can be very different from the actual internal temperature of the battery--the truly desired quantity. These temperature differences come about from localized internal heating caused by currents flowing through the battery, from the large thermal mass of the battery, and from the poor thermal contact between the battery and its environment. For example, an automobile engine compartment will warm up rapidly with the engine running. If the battery is cold, however, its internal temperature will remain low for a very long period of time.